... explicitly1
In our prototype implementation we provide sample scatter/gather routines. 
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... domain2
This is the normal situation when the pattern of the sparse matrix is symmetric, which is equivalent to say that the interaction between two variables is reciprocal. If the matrix pattern is non-symmetric we may have one-way interactions, and these could cause a situation in which a boundary point is not a halo point for its neighbour. 
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... follows3
The string is case-insensitive 
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... method4
Note: the implementation is for $FCG(1)$. 
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